/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package ai.platon.pulsar.common;

import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import java.util.Stack;

/**
 * <p>
 * A utility class that allows the walking of any DOM tree using a stack instead
 * of recursion. As the node tree is walked the next node is popped off of the
 * stack and all of its children are automatically added to the stack to be
 * called in tree order.
 * </p>
 * <p>
 * Currently this class is not thread safe. It is assumed that only one thread
 * will be accessing the <code>NodeWalker</code> at any given time.
 * </p>
 *
 * @author vincent
 * @version $Id: $Id
 */
public class NodeWalker {

    // the root node the the stack holding the nodes
    private Node currentNode;
    private NodeList currentChildren;
    private Stack<Node> nodes;

    /**
     * Starts the <code>Node</code> tree from the root node.
     *
     * @param rootNode a {@link org.w3c.dom.Node} object.
     */
    public NodeWalker(Node rootNode) {

        nodes = new Stack<Node>();
        nodes.add(rootNode);
    }

    /**
     * <p>
     * Returns the next <code>Node</code> on the stack and pushes all of its
     * children onto the stack, allowing us to walk the node tree without the use
     * of recursion. If there are no more nodes on the stack then null is
     * returned.
     * </p>
     *
     * @return Node The next <code>Node</code> on the stack or null if there isn't
     * a next node.
     */
    public Node nextNode() {

        // if no next node return null
        if (!hasNext()) {
            return null;
        }

        // pop the next node off of the stack and push all of its children onto
        // the stack
        currentNode = nodes.pop();
        currentChildren = currentNode.getChildNodes();
        int childLen = (currentChildren != null) ? currentChildren.getLength() : 0;

        // put the children node on the stack in first to last order
        for (int i = childLen - 1; i >= 0; i--) {
            nodes.add(currentChildren.item(i));
        }

        return currentNode;
    }

    /**
     * <p>
     * Skips over and removes from the node stack the children of the last node.
     * When getting a next node from the walker, that node's children are
     * automatically added to the stack. You can call this method to remove those
     * children from the stack.
     * </p>
     * <p>
     * <p>
     * This is useful when you don't want to process deeper into the current path
     * of the node tree but you want to continue processing sibling nodes.
     * </p>
     */
    public void skipChildren() {

        int childLen = (currentChildren != null) ? currentChildren.getLength() : 0;

        for (int i = 0; i < childLen; i++) {
            Node child = nodes.peek();
            if (child.equals(currentChildren.item(i))) {
                nodes.pop();
            }
        }
    }

    /**
     * Return the current node.
     *
     * @return Node
     */
    public Node getCurrentNode() {
        return currentNode;
    }

    /**
     * * Returns true if there are more nodes on the current stack.
     *
     * @return a boolean.
     */
    public boolean hasNext() {
        return (nodes.size() > 0);
    }
}
